In the past fifty years, ink jet printing has matured from a technical curiosity to a mainstay of office automation. Advances in recent years have permitted ink jet printers to produce print quality that rivals that of laser printers. Nonetheless, the existing state of the art has certain deficiencies.
One deficiency is in the area of color printing. The basic art of ink jet color printing is well developed. It basically entails controllably ejecting droplets of cyan, yellow, magenta and sometimes black ink from separate printheads towards the printing medium. Such printing, however, requires precise relative positioning of each individual printhead so that the ink droplets produced thereby will land on the printing medium in the desired spatial relationship with the droplets produced by the other printheads. One approach to this precise relative positioning requirement has been to fabricate some or all of the printheads into one assembly, using a single orifice plate in which all the necessary orifii are formed. Since the orifice plate is formed photolithographically, the relative positioning of the various component printheads can be achieved with a high degree of accuracy. Unfortunately, the fabrication of several printheads into one assembly renders the assembly virtually useless when the first of the ink supplies in the printhead runs dry.
Another approach to the precise relative positioning requirement is to use several discrete printheads and to optically inspect the position of the orifice plate on each printhead after it has been mounted in a printer. In one such system, shown in U.S. Pat. No. 4,709,245, the edges of each orifice plate are detected by moving each printhead past a light source and sensing changes in the reflected light. If the orifice plates have been fabricated by a process in which the edges of the plate are accurately defined, such as by photolithography, then this technique can be useful in characterizing the locations of the printing orifii in the horizontal direction. However, it provides no information about the vertical position of the orifices. Furthermore, the technique is ineffective if the edges of the orifice plate are not precisely defined, as is often the case when the plate is simply sawn from its parent die.
A related deficiency in color printers is the untimely exhaustion of ink of one color during a long and complex printing task. The printing of a complex color graphic image may take several minutes. If one of the constituent inks becomes exhausted, the task must be interrupted, the exhausted printhead replaced and the task started anew. This is a waste not only of time, but also of the ink of the other colors that was used in the aborted printing task.
Some attempts have been made at providing visual indicia to indicate when an ink jet printhead is nearing exhaustion. Exemplary are ink jet printheads with transparent ink chambers. However, manufacturing considerations often dictate that opaque materials be used.
Still another deficiency of color printing systems, at least those involving separate printheads for the constituent colors, is in the inadvertent misplacement of printheads in the printer. If the cyan ink printhead is positioned where the magenta ink printhead belongs, the resulting print will be unacceptable.
The present invention addresses these and other shortcomings of prior art ink jet printing systems by providing in association with each printhead a memory element in which data characterizing the printhead can be stored. This data can characterize the identity of the printhead, or one or more of its operational characteristics. Such operational characteristics may include the color of ink in the printhead, its amount, or the position of the orifice plate on the printhead body. This data can then be read from the printhead and used or displayed as desired. The datum characterizing the position of the orifice plate, for example, can be used to controllably advance or delay certain of the orifice firing signals to compensate for any misalignment. The datum characterizing ink color can be used to permit the printer to receive printheads of any color at any printhead receptacle. The datum characterizing ink amount can be updated to reflect use of ink during printing and can warn the user of an impending exhaustion of ink.
The foregoing and additional objects, features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.